/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.base;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;

import java.io.Serializable;
import javax.annotation.CheckForNull;

/**
 * Equivalence applied on functional result.
 *
 * @author Bob Lee
 * @since 10.0
 */
@Beta
@GwtCompatible
@ElementTypesAreNonnullByDefault
final class FunctionalEquivalence<F, T> extends Equivalence<F> implements Serializable
{

    private static final long serialVersionUID = 0;

    private final Function<? super F, ? extends T> function;
    private final Equivalence<T> resultEquivalence;

    FunctionalEquivalence(
            Function<? super F, ? extends T> function, Equivalence<T> resultEquivalence)
    {
        this.function = checkNotNull(function);
        this.resultEquivalence = checkNotNull(resultEquivalence);
    }

    @Override
    protected boolean doEquivalent(F a, F b)
    {
        return resultEquivalence.equivalent(function.apply(a), function.apply(b));
    }

    @Override
    protected int doHash(F a)
    {
        return resultEquivalence.hash(function.apply(a));
    }

    @Override
    public boolean equals(@CheckForNull Object obj)
    {
        if (obj == this)
        {
            return true;
        }
        if (obj instanceof FunctionalEquivalence)
        {
            FunctionalEquivalence<?, ?> that = (FunctionalEquivalence<?, ?>) obj;
            return function.equals(that.function) && resultEquivalence.equals(that.resultEquivalence);
        }
        return false;
    }

    @Override
    public int hashCode()
    {
        return Objects.hashCode(function, resultEquivalence);
    }

    @Override
    public String toString()
    {
        return resultEquivalence + ".onResultOf(" + function + ")";
    }
}
